Research on the Island of Trinidad, Republic of Trinidad
& TobagoJim Reynolds and Sam Algar

Fishermen from the Port-of-Spain area travel
far offshore. These men are near the international border with Venezuela,
seen in the background. I was aboard a racing yacht with Sam and a Trinidadian
businessman, the late David Farfan. It was an exhilarating day that ranged
from strong winds to being becalmed after sunset.

The northwest peninsula of Trinidad was once connected to the South
American mainland. As a result, it is the only island of the Lesser Antilles
that has indigenous South American animals living on it. These include
jaguars, boa constrictors, bushmasters, and fer-de-lances.

The site of our 1992 project was at Galeota Point,
at the southeastern corner of the island. To get there, one must drive
eastward from Port-of-Spain to the Atlantic coast and then drive southward
to Galeota Point. Much of the shoreline has been shaped by longshore drift
so most of the river mouths are cut off from the sea by baymouth bars.
The lagoons behind these bars are steadily becoming mangrove swamps as
more and more trees take root.

Galeota Point isn't quite at the corner of the
island but it is pretty close to it. Amoco has a large petroleum terminal
located above the beach, just to the right of this photo. Sam Algar, then
a Dartmouth doctoral student, Jaime Zera, one of my Norwich undergraduate
students, and I took magnetostratigraphy samples through about 800 m of
strata exposed along the beach.

At low tide, we could scramble across the slippery
rocks to the lowest part of the exposed section. The strata are Upper Miocene
deltaic sandstones and shales that were deposited on the subsiding Orinoco
Delta off the coast of Venezuela. Right-lateral transpression between the
Caribbean Plate and the South American Plate caused the uplift and deformation
of the island of Trinidad. The plate boundary is located just off of the
north coast of the island.

Included in the section are some spectacular
exposures of soft sediment deformation. This was probably caused when earthquakes
along the plate boundary triggered underwater sediment slumping and landslides.

We ran out of outcrop somewhere above the Plio-Pleistocene
boundary. We estimate that the oldest rocks at Galeota Point, in the distance,
are around 5.5 million years old (Upper Miocene) and that the youngest
rocks are under a million years old. This suggests that the petroleum in
this area was probably generated during the late Pliocene and Pleistocene.

One day we went to the southeastern corner of
the island at Guayaguayare. At low tide, we slipped around the corner hoping
to find vast exapanses of outcrop to sample. Instead, all we found was
this short deserted beach with further access cut off by the cliff in the
background. We took a few samples and returned around the corner before
the tide rose. The first Europeans to see this beach were probably Columbus
and his crew on one of his later voyages. Columbus named Trinidad for the
Holy Trinity because from the east one can see the island's Northern, Central,
and Southern ranges.

A fascinating and unusual geological phenomenon
is present on the southwestern coast of Trinidad at La Brea. La Brea means
tar in Spanish. A diapir of natural asphalt is being pushed up to the surface.
It was discovered by Sir Walter Raleigh and became a stopover point for
wooden ships visiting the New World so that they could recaulk their hulls.
The British began mining it more than a century ago; many of the roads
in Britain are paved with this stuff! The mining procedure is fascinating.
Bulldozers rip up the asphalt to a depth of several meters. After refining,
it is trucked across the dunes to waiting ships. Over the next month or
two, the asphalt body rises to its former level and the mining procedure
is repeated.

Maracas Bay is situated on the Caribbean North
Shore of Trinidad, just north of Port-of-Spain. The plate boundary between
the Caribbean and South American plates is just several kilometers off
shore. Trinidad is on the South American Plate while Tobago, the sister
island in the Republic of Trinidad & Tobago, is situated on the Caribbean
plate. Unlike the Central and Southern ranges which are composed of sedimentary
rocks, the Northern range, shown here is made of low-grade metamorphic
rocks.